The photochemistry of  NO and CF3I has been studied in Ar matrices at temperatures of 12-13 K. The matrix ratios in each experiment were relatively concentrated at 259:1 (Ar:NO)  and 144:1 (Ar:CF3I). No was irradiated at 632 nm with a helium-neon laser then using a UV lamp with various filters. Irradiation generated the predominant cis-(NO)2 dimer as well as the more elusive asymmetrical ON-ON dimer. Investigation of the peak areas of the nitrogen oxides trapped in the matrix and energy calculations indicate that a plausible mechanism for ON-ON formation involves the intraconversion of the cis-(NO)2 dimer. The fundamental peaks for CF3I were also observed, however, irradiation with a deuterium lamp failed to generate noticeable CF3 radical peaks. This was attributed to the high concentration of CF3I in the matrix which caused the CF3I peaks to broaden and overlap those associated with CF3.